Theory behind view dependant IRmaps

[jmottle]

I was having a discussion with someone last night and the topic of saved photon/irrandiance maps came up and I wanted to know the theory behind this.

For example renderers like MAX/VIZ have view independant indirect illumination, but Vray only renders what is visible to the camera. In both cases the entire scene has to be accounted for during the calculation of what is visible to the camera anyway, so why is one view dependant and the other view indepenant?

What are the advantages to one way over the other given that both are Photon Map GI renderers?

Cheers,
Jeff

[plastic_]

photon mapping is like radiosity...calculated for the whole scene.
the irradiance and lightmap is only calculated for the visible part of the scene. the advantage is that it's faster and doesn't need as much memory, so typically it can be more detailled than photon maps/radiosity.

[vlado]

Well, VRay is not a photon map renderer, although it can use photon maps. I'll try to write a more detailed description tonight...

Best regards,
Vlado

[losbellos]

here is simply:

radiosity: adv:, view indepent, even realtime viewing possible.
dadv: Takes very long time to compute, need special tesselation, not really easy to set up.

photon map: adv: very fast and simple, view indenpendent.
dadv:, takes quite some memory, usually only good for secondary illumination approximation. Corners, small objects are problematic.

irradiance chache(irradiance map): So far the best GI implementation. Fast, takes little memory, very controllable, smooth result.
dadv:not view independent, but possible.

quasi monte carlo, Adv: very accurate, takes little memory
dadv: very slow.

well, there are other technics to simulate the illumination. But these are most popular by now and at least few more years.

[vlado]

Here is a more detailed classification of GI methods, I hope it can be useful. If you think something should be added, let me know:

http://www.vrayrender.com/stuff/gimethods/gimethods.htm

Best regards,
Vlado

[jmottle]

Awesome thanks Vlado!